Although you may just now be hearing about acute flaccid myelitis, it is important to understand that it isn’t new.

The rise in AFM cases began in 2014 and seem to occur every other year.

It wasn’t even new when we started to see an increased number of cases a few years ago.

What is new, is that we are seeing an increased number of cases.

Acute Flaccid Myelitis Timeline

AFM refers to acute (sudden onset) flaccid (droopy or loose muscles) myelitis (inflammation of the spinal cord) and it is a subtype of acute flaccid paralysis.

If that explanation doesn’t really help you, it might help to understand that paralytic polio, like AFM, is another subtype of acute flaccid paralysis.

“In August 2012, the California Department of Public Health (CDPH) was contacted by a San Francisco Bay area clinician who requested poliovirus testing for an unvaccinated man aged 29 years with acute flaccid paralysis (AFP) associated with anterior myelitis (i.e., evidence of inflammation of the spinal cord involving the grey matter including anterior horn cell bodies) and no history of international travel during the month before symptom onset. Within 2 weeks, CDPH had received reports of two additional cases of AFP with anterior myelitis of unknown etiology.”

Unfortunately, they didn’t figure out what was causing the paralysis in these three patients, despite extensive testing and more cases followed.

“To identify other cases of AFP with anterior myelitis and elucidate possible common etiologies, CDPH posted alerts in official communications for California local health departments during December 2012, July 2013, and February 2014.”

Among 23 cases, California health officials found that the median age of the patients was 10 years old, only two tested positive for EV-D68, although most did have a recent “an upper respiratory or gastrointestinal prodrome.”

“Acute flaccid paralysis (AFP) with anterior myelitis is not a reportable condition, and baseline rates of disease are unknown but are likely quite low. Data from 1992–1998 on children aged <15 years in California indicated an incidence of 1.4 AFP cases per 100,000 children per year and did not identify a single case of AFP with anterior myelitis.”

California wasn’t the only state with cases.

In 2014, there were at least 12 cases in Colorado and 11 in Utah.

“In response to the CDPH and CHCO reports, the CDC established a case definition for enhanced nationwide surveillance of AFM, which included individuals less than 21 years of age with acute flaccid limb weakness and MRI involvement of predominantly the gray matter of the spinal cord without identified etiology presenting after August 1, 2014.”

All together though, in 2014, once the CDC began actively investigating cases, at least 120 cases were discovered in 34 states. The cases were associated with a large outbreak of EV-D68-associated respiratory illness, although they weren’t able to conclusively link those respiratory illnesses to the AFM cases.

Is there any evidence that there were a lot of cases before 2012?

Or that the CDC has dropped the ball and hasn’t been doing enough to investigate cases?

CDC activities include… using multiple research methods to further explore the potential association of AFM with possible causes as well as risk factors for AFM. This includes collaborating with experts to review MRI scans of people from the past 10 years to determine how many AFM cases occurred before 2014, updating treatment and management protocols, and engaging with several academic centers to conduct active surveillance simultaneously for both AFM and respiratory viruses.

CDC on the AFM Investigation

And if the first cases in California and Colorado triggered so much attention, isn’t it likely that any cases anywhere else would have done the same thing?

That makes it very unlikely that many cases were missed in earlier years.

EV-D68 first identified as a cause of respiratory tract infections – 1962

the first reports that EV-D68 could cause severe, even fatal respiratory disease – 2008

first AFM cases are discovered in California – August 2012

the Colorado Department of Public Health and Environment notifies the CDC about a cluster of AFM cases at Children’s Hospital Colorado and a joint investigation begins between the CDPH, CDC, and the physicians caring for the patients – September 2014

the CDC issues a health advisory on Acute Neurologic Illness with Focal Limb Weakness of Unknown Etiology in Children and calls on local and state health departments to report patients to the CDC – September 2014

the CDC conducts a conference call on Neurologic Illness with Limb Weakness in Children, so that clinicians could learn about the latest situation, surveillance, and CDC clinical guidance for AFM testing, patient evaluation and case reporting – October 2014

CDC Telebriefing on Acute Flaccid Myelitis in the US with Dr. Nancy Messonnier, director of CDC’s National Center for Immunization and Respiratory Diseases – August 2018

158 AFM cases confirmed in 36 states among 311 reported cases that are being investigated – 2018

The other issue that concerns many parents is why a definitive cause hasn’t yet been identified. And why don’t we have treatments or a cure yet?

“To date, no pathogen (germ) has been consistently detected in the patients’ spinal fluid; a pathogen detected in the spinal fluid would be good evidence to indicate the cause of AFM since this condition affects the spinal cord.”

CDC on AFM Investigation

Although enteroviruses can be difficult to detect in spinal fluid, it is important to keep in mind that isn’t the only thing that is keeping experts from declaring the investigation over and naming a cause, such as EV-D68.

Eyal Leshem on Notes from the Field: Acute Flaccid Myelitis Among Persons Aged ≤21 Years — United States, August 1–November 13, 2014

Another big issue is that EV-D68 has not been detected in every, or even most AMF patients, and many others have been found to have other enteroviral infections, including EV-A71.

Could it be a coincidence that investigators are finding these enteroviruses simply because it is the season for them to appear? That would mean something else is causing these kids to have AFM.

“During September–November 2016, 10 confirmed cases of AFM were reported in Washington. No common etiology or source of exposure was identified. Enterovirus-A71 was detected in one patient and EV-D68 in two patients, one of whom also tested positive for adenovirus.”

While the focus is on EV-D68 as a cause and everyone wants an answer, no one wants the CDC or other investigators to be wrong.

That doesn’t mean that they should be overly cautious and waste time or resources once an answer is evident, but just that they should follow sound epidemiological principles, get the right answer, and help stop kids from getting AFM.

What’s Next for AFM?

There are still a lot of unknowns about AFM, but this is likely what we can expect in the coming months:

the CDC will continue to investigate all unconfirmed cases that have occurred this year, which can take about four weeks after a case is reported and all necessary information is sent in. Keep in mind that since we don’t know if the CDC has already received all of the information on the cases they are investigating, we don’t know when they will finish investigating any pending cases.

local or state health departments will likely reach out to treating physicians to get followup about AFM patients about two months after they developed limb weakness and then report this short-term follow-up data to the CDC. In general, the CDC does not seem to contact patients directly.

From the current investigation, information from outbreaks and cases over the previous years, and cases in other countries, we will hopefully get the answers we need soon to prevent and treat AFM.

The AFM Surveillance Team will participate in a COCA Call in mid-November.

Maybe some of those answers will come during a Clinician Outreach and Communication Activity (COCA) Call on November 13, when members from the CDC Acute Flaccid Myelitis Surveillance Team discuss the “activities the CDC is conducting as part of its investigation into AFM.”

The fact that the CDC has an Acute Flaccid Myelitis Surveillance Team will be news and is hopefully reassuring to some folks…

This is also probably a good time to remind folks that funding for public health has been declining in recent years, even as we expect our public health officials to respond to more things and react more quickly to keep us all safe and healthy. Let’s make sure we fund our public health programs, including the CDC and NIH, so that they have all of the resources they need to address all of today’s public health challenges.